Suitability of saturated aldehydes as lipid oxidation markers in washed turkey meat

The aim of this study was to evaluate the suitability of saturated aldehydes as lipid oxidation markers in washed turkey muscle, by means of headspace solid phase microextraction-gas chromatography (HS-SPME-GC); the results were compared with the widely used thiobarbituric acid-reactive substances (TBARs) method. Changes in TBARs, propanal and hexanal concentrations were determined over time in a model system consisting of turkey muscle washed with a sodium phosphate buffer (pH 5.6). To stop oxidation from occurring during analysis, an antioxidant mixture (EDTA, trolox and propyl gallate) was added immediately before analyses. After antioxidant addition, propanal and TBARs concentrations did not increase during 8 h of further storage, while an unexpected decrease in hexanal was observed. To determine if aldehydes were interacting with washed turkey muscle, hexanal and propanal were added to either phosphate buffer or washed muscle and concentrations were monitored for 24 h. Neither propanal nor hexanal decreased in the phosphate buffer over time, but the headspace concentration of propanal and hexanal in washed turkey muscle were markedly lower (76% and 96%, respectively) at time zero and continued to decreased up to 24 h of storage. Because of this decrease in headspace aldehyde concentrations, TBARs were found to be a more sensitive and accurate marker of oxidative deterioration in washed turkey muscle.     

β-葡聚糖糖基化对裸燕麦蛋白功能性质及抗氧化活性的影响

使用β-葡聚糖对裸燕麦蛋白进行糖基化处理,测定裸燕麦蛋白糖基化反应前后的功能性指标,观察糖基化改性过程中复合物的生成情况,分析糖基化改性作用机理,进行体外抗氧化实验。结果表明:在pH5、7、9、11环境中,糖基化反应后的裸燕麦蛋白溶解性均得到改善,pH5环境下提高了3.06倍,pH3~11范围内糖基化裸燕麦蛋白的起泡性提高明显,pH5环境下提高了5倍,在pH5环境下,糖基化裸燕麦蛋白的乳化性及乳化稳定性分别提高了2.48及2.59倍;SDS-PAGE凝胶电泳发现,糖基化改性后有大分子物质生成,内源荧光光谱分析表明糖基化反应过程中体系环境转向亲水性,红外光谱分析反映了蛋白与糖分子之间的共价结合,在圆二色谱中观察到糖基化反应改变了蛋白的二级结构;浓度为10 mg/mL时,糖基化裸燕麦蛋白DPPH·清除率是原蛋白的2.13倍,浓度为2.5 mg/mL时,糖基化裸燕麦蛋白ABTS+·清除率是原蛋白的2.09倍。裸燕麦蛋白与β-葡聚糖的糖基化反应改变了蛋白质的结构,复合物转向亲水性,功能性得到改善,且抗氧化活性也强于原裸燕麦蛋白。     

茶多酚对酸奶发酵品质及抗氧化活性的影响

目的：研究茶多酚对酸奶发酵品质及抗氧化活性的影响。方法：对含有不同浓度茶多酚(0、0.1、0.2、0.3、0.4和0.5 g/100 mL牛乳)的牛乳进行发酵以制作酸奶。通过理化分析实验测定茶多酚对酸奶的pH、可滴定酸度、营养成分含量、持水力的影响,利用质构仪、色差色度仪、顶空固相微萃取-气相色谱-质谱联用分析茶多酚对酸奶的质构特性、颜色和风味成分的影响,通过高效液相色谱法分析酸奶发酵过程对茶多酚中四种儿茶素含量的影响,并通过体外抗氧化实验测定了茶多酚酸奶的抗氧化能力。结果：茶多酚对酸奶的pH、可滴定酸度和营养成分的影响不显著;茶多酚的添加使酸奶的持水力、硬度、黏性、胶粘性和内聚性略微降低,并使得酸奶的颜色略微偏红和偏黄;茶多酚的添加使得酸奶中的酸类风味物质的含量略有降低,而酮类和醇类风味物质的种类和含量有所增加;酸奶发酵过程中,酯化儿茶素(表没食子儿茶素没食子酸酯和表儿茶素没食子酸酯)发生了降解,非酯化儿茶素(表儿茶素和表没食子儿茶素)的变化不明显;体外抗氧化实验表明,茶多酚的添加可以显著提高酸奶的抗氧化活性(包括：DPPH及ABTS⁺自由基清除能力和还原能力的...     

Solubility and functional properties of sesame seed proteins as influenced by pH and/or salt concentration

The protein content, solubility and functional properties of a total protein isolate prepared from sesame seeds (Kenana 1 cultivar) as a function of pH and/or NaCl concentration were investigated. The protein content of the seed was found to be 47.70%. The minimum protein solubility was at pH 5 and the maximum was at pH 3. The emulsifying capacity, activity and emulsion stability as well as foaming capacity and foam stability were greatly affected by pH levels and salt concentrations. Lower values were observed at acidic pH and high salt concentration. The protein isolate was highly viscous and dispersable at pH 9 with water holding capacity of 2.10 ml H₂O/g protein, oil holding capacity of 1.50 ml oil/g protein and bulk density of 0.71 gm/ml.     

FUNCTIONAL PROPERTIES OF HIGH HYDROSTATIC PRESSURE-TREATED WHEY PROTEIN

Surface hydrophobicity, solubility, gelation and emulsifying properties of high hydrostatic pressure (HHP)‐treated whey protein were evaluated. HHP treatment of whey protein buffer or salt solutions were performed at 690 MPa and initial ambient temperature for 5, 10, 20 or 30 min. Untreated whey protein was used as a control. The surface hydrophobicity of whey protein in 0.1 M phosphate buffers treated at pH 7.0 increased with an increase in HHP treatment time from 10 to 30 min. HHP treatments of whey protein in salt solutions at pH 7.0 for 5, 10, 20 or 30 min decreased the solubility of whey proteins. A significant correlation was observed between the surface hydrophobicity and solubility of untreated and HHP‐treated whey protein with r = ?0.946. Hardness of HHP‐induced 20, 25 or 30% whey protein gels increased with an increase in HHP treatment time from 5 to 30 min. An increase in the hardness of whey protein gels was observed as whey protein concentration increased. Whey proteins treated in phosphate buffer at pH 5.8 and 690 MPa for 5 min exhibited increased emulsifying activity. Whey proteins treated in phosphate buffer at pH 7.0 and 690 MPa for 10, 20 or 30 min exhibited decreased emulsifying activity. HHP‐treated whey proteins in phosphate buffer at pH 5.8 or 7.0 contributed to an increase in emulsion stability of model oil‐in‐water emulsions. This study demonstrates that HHP treatment of whey protein in phosphate buffer or salt solutions leads to whey protein unfolding observed as increased surface hydrophobicity. Whey proteins treated in phosphate buffers at pH 5.8 and 690 MPa for 5 min may potentially be used to enhance emulsion stability in foods such as salad dressings, sausage and processed cheese.     

Solubility and Foaming Properties of Phytate-Reduced Soy Protein Isolate

A pilot scale ion exchange process was developed to produce a 75 - 77% phytate-reduced soy protein isolate. The solubility and foaming properties of this isolate were compared to those of control and commercial soy protein isolates as a function of protein concentration (5 and 10%, w/v), pH (3, 6 and 9) and preheat temperature (25, 60 and 80°C). Phytate-reduced soy protein extract exhibited minimum solubility at pH 4.8 - 5.0, compared to 4.2 - 4.5 for control soy extract. Phytate-reduced soy protein isolate was most soluble and functional at pH values below its isoelectric point (pH 3), whereas control and commercial soy isolates were generally most soluble and functional at pH values above their isoelectric point (pH 6 and 9).     

Functional and antioxidant activity of <Emphasis Type="Italic">Ziziphus jujube</Emphasis> seed protein hydrolysates

Ziziphus jujuba is a medicinal plant with well demonstrated biological functions for which various bioactive compounds except antioxidants peptides from seeds have been reported. Therefore, the aim of this study was to determine antioxidant activity, metal ion chelation and reducing power of Z. jujuba seeds-derived protein hydrolysate. The concentration of protein was 5.72 mg/g in 50 mM Tris-HCl buffer pH 7.5. The solubility of protein was above 90 % at pH 2 and 3, decreased at pH 4 and subsequently increased further with an increase in pH. The seed derived protein showed an excellent solubility and possessed interfacial properties, which were governed by their concentrations. The antioxidant activities of protein hydrolysate were evaluated using various in vitro antioxidant assays. Alcalase, papain and protease hydrolysate shows (8.09, 9.14 and 8.92 µM of TE/g) antioxidant capacity by ABTS and radical scavenging activity (7.21, 17.54 and 8.36) by DPPH. From this study, it was observed that the papain hydrolysate of Ziziphus jujube is a good source of natural antioxidants and peptides with interesting functionalities.     

Solubility and emulsifying properties of barley protein concentrate

Protein concentrates were produced from the flours of two barley cultivars (Bülbül and Tokak) by alkaline extraction procedure. The flour samples and their protein concentrates were examined by SDS-PAGE. Solubility properties of protein concentrates were investigated as a function of pH, NaCl concentration and protein concentration, whereas emulsifying properties were determined as a function of pH and protein concentration. The highest solubility was observed in water among the solvents studied, especially at pH values of 2, 10 and 11 as compared to the other ones. A decrease in solubility was determined with increasing ionic strength of NaCl solutions. The results suggested that emulsifying behavior of protein concentrates generally resembled their solubility behavior in water. Minimum solubility and emulsifying values were observed at pH 6, which is close to the isoelectric point of barley proteins. Both of these functional properties were improved below and above the isoelectric pH.     

Viscosity and Stability of Structural Proteins of Irradiated Indian Mackerel

Fresh Indian mackerel (Rastrelliger kanagurta) was exposed to gamma radiation at dosages of 0,1.5 and 3 kGy. The meat was collected and subjected to a four-step washing treatment. Homogenates of the washed meat in cold (<10°C) water exhibited apparent viscosity, which was dependent upon protein concentration. Warming the homogenate to 45°C or reduction of its pH to 3.5 by acetic acid decreased the viscosity. Proteins in the low-viscosity dispersion were stable to heating at 100°C while incorporation of NaCl at 5 mM prior to heating resulted in protein precipitation. Gamma irradiation did not affect the viscosity, solubility or stability of the muscle proteins in water.     

胡麻籽分离蛋白的溶解性与起泡性研究

为促进胡麻籽分离蛋白在食品工业中的应用,研究了pH值、盐浓度、蛋白质浓度等因素对其水溶性、起泡性和泡沫稳定性的影响。pH值对胡麻籽分离蛋白溶解度的影响呈典型的V形曲线。NaCl浓度为0.4mol/L前后胡麻籽分离蛋白表现出明显的盐溶与盐析效应。在0.1%～0.8%范围内,提高蛋白质浓度能增强起泡性与泡沫稳定性。在等电点附近,胡麻籽分离蛋白的起泡性最差但却具有最强的泡沫稳定性。NaCl对胡麻籽分离蛋白的起泡性的影响与其对溶解性的影响有相同的趋势。蔗糖能提高胡麻籽分离蛋白的泡沫稳定性,但当浓度高于5%时,对起泡性有负面影响。     

超高压处理对花生分离蛋白溶解性影响

该实验研究超高压对花生分离蛋白溶解性影响,测定不同压力、加压时间、蛋白浓度、pH值时花生分离蛋白溶解性。结果表明:花生分离蛋白随处理压力升高和处理时间延长,其溶解性提高;花生分离蛋白浓度越高,溶解度也越大;在pH 6～9范围内,花生分离蛋白溶解性随pH增加而增大。     

大豆蛋白凝胶制备及其性质研究

研究以NaCl作为凝固剂,将大豆分离蛋白(SPI)80℃预热处理10 h,在不同浓度、离子强度及pH值条件下,通过95℃加热蛋白液30min使蛋白变性来制备大豆蛋白凝胶,并对凝胶的质构及凝胶特性进行了分析。结果表明:pH值7.0、80℃预热处理10 h的大豆蛋白溶解性明显小于普通SPI,其他pH值条件下两者溶解性差异不大;pH值2.0、80℃预热处理10 h的蛋白凝胶情况明显优于普通SPI,在一定范围内,随着蛋白浓度及离子强度的增加,凝胶情况越来越好。     

Effect of pH on the properties of soy protein–pectin complexes

The interactions of a commercial soy protein isolate (SPI) and a 2:1 SPI:high methoxy pectin (PEC) complex were evaluated over a range of pH values (3-7). The SPI formed very large (> 50 ??m) and largely insoluble aggregates (< 10%) close to its isoelectric point (IEP, pH 4 and 5) and smaller, more soluble (> 80%) particles at higher and lower pH values. The addition of PEC increased the solubility of SPI close to its IEP (pH 4 and 5) and prevented the formation of very large aggregates. However, PEC reduced the solubility of SPI at higher and lower pH values presumably via a depletion mechanism. The ??-potential of diluted SPI dispersions decreased from positive to negative with increasing pH, passing through zero at pH 4.6, the isoelectric point (IEP) of the protein. At pH < 6, the addition of PEC reduced the charge of the protein suggesting the formation of a complex while at pH 6 or 7 there was no evidence of complex formation. The increased SPI solubility in the IEP in the presence of PEC is probably due to the formation of charged complex which do not aggregate while the decreased solubility of protein in the presence at high and low PEC is probably due to the formation of insoluble complexes and a depletion interaction respectively. Thermal treatment (30 min, 90 °C) enhanced the solubility of the SPI:PEC complexes close to the IEP (pH 4 and 5), but reduces it at low pH (pH 3). The SPI:PEC complexes could be manufactured in the form of a beverage at pilot scale where their solubility was enhanced by homogenization.     

黄粉虫幼虫蛋白质的提取研究

研究了不同的介质pH值、提取时间、提取温度和加水比例对黄粉虫幼虫蛋白质的可溶出率(提取率)的影响,分析了3种不同pH值提取的蛋白质的氨基酸组成。结果表明,pH值极大地影响着黄粉虫幼虫蛋白质的溶出率,pH值5.8时溶出率最低,此时可能为黄粉虫蛋白的等电点;pH值10.0或高于此值具有较高的溶出率;水与虫之比为10时蛋白质的可溶出率较其它比例为高;其它的因素对幼虫蛋白质的溶出率影响不大。在pH值2.4、5.8和12.1下提取的蛋白质其氨基酸组成不同,提取的黄粉虫蛋白质必需氨基酸占总氨基酸的含量达40％以上。     

On the functional properties of globulin and albumin protein fractions and flours of African locust bean (Parkia biglobossa)

Albumin (ALBa) and globulin (ALBg) fractions of African locust bean were isolated and the functional properties were compared with its defatted (ALBdf) and undefatted flours (ALBf). Albumin had minimum % solubility (56.7%) at pH5, while minimum solubility was observed at pH4 for globulin and the flours. In all the samples studied, maximum solubility was observed at pH 10. A pH-dependent gelation study revealed that all of the samples had the highest least gelation concentration at pH10 apart from ALBf which had 16% w/v LGC at pH 2. Initial increase in ionic strength of the medium, to 0.4 and 0.6 M, enhanced the gelation capacity of protein fractions and flours, respectively, while further increase in ionic strength reduced it. Oil absorption capacity was maximal in ALBa while ALBf had the least value of 1.05 ml/g. Initial increase in ionic strength, up to 0.4 M, increased the water absorption capacity (WAC) of albumin fractions while WACs of the globulin fraction and flours were reduced when the ionic strength of the media reached 0.4 M. Foam capacity increased as the concentration of protein solution increased but was reduced by 6% w/v in ALBf. Initial increase in ionic strength enhanced both foam capacity and stability. Maximum EA was observed at pH 10 in all samples apart from ALBf, which reached a peak EA value at pH 2. ES (emulsion stability) was maximal at pH 10 for ALBa and ALBg while the same values were observed for ALBdf and ALBf at pH 2 and 10. Increasing the ionic strength, to 0.4 M, enhanced the EA and ES of ALBa while further increase in ionic strength, to 0.7 M, improved EA of ALBf but reduced the ES. Both EA and ES of ALBf reached peak values in 0.2 M solutions but no fixed pattern was observed in the response of ALBdf to various ionic strengths of the solutions.     

GREEN TEA CATECHINS AS INHIBITORS OF OXIDATION OF MEAT LIPIDS

Antioxidant activity of green tea catechins, namely, epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) was evaluated in a meat model system. The inhibitory effect on 2-thiobarbituric acid (TBA) values of catechins was concentration dependent, being highest at 200 mg/kg. At 200 mg/kg, the antioxidant activity of catechins as evaluated by TBA values was EGCG ≈ ECG > EGC > EC. The hexanal and pentanal contents in the headspace volatiles of meats treated with catechins at 200 mg/kg was also evaluated. These results indicated that EGCG was most active followed by ECG and EGC; EC was least effective. In comparison with α-tocopherol, catechins were generally more effective in controlling oxidation of meat lipids. Based on TBA results, butylated hydroxytoluene (BHT) was less effective, but exerted a better effect than catechins in prevention of oxidation as evidenced by the hexanal/pentanal data.     

美藤果蛋白的功能性质研究

以美藤果饼为原料,采用碱提酸沉法制备美藤果蛋白,研究pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白功能性质的影响。结果表明:当pH为5时,美藤果蛋白的溶解度、乳化性能和起泡性均最小;随着温度的升高,美藤果蛋白的溶解度、持水性、持油性呈先增大后减小的趋势;加入适量NaCl可增大美藤果蛋白的溶解度、乳化性能和起泡性能;加入蔗糖使美藤果蛋白的起泡性降低,而加入适量的蔗糖可增大美藤果蛋白的乳化性能。pH、温度、NaCl浓度和蔗糖浓度对美藤果蛋白的功能性质有一定影响,可通过改变上述条件以获得良好加工性质的美藤果蛋白产品。     

多指标优化珠蚌抗氧化肽制备工艺

采用取珠后珠蚌肉为原料,选用木瓜蛋白酶进行水解。以DPPH自由基清除率、.OH清除率及蛋白水解度作为评价指标,研究珠蚌抗氧化活性肽的制备工艺。在单因素基础上,通过三个指标的综合考虑,设计L18(37)多指标正交试验,对制备工艺进行优化,得出最佳工艺条件。结果表明,最佳条件为:酶解温度60℃、酶解时间5h、料液比3:10(w/v)、酶解pH6.5、加酶量6000U/g,制得的多肽DPPH自由基清除率85.5%,.OH清除率50.7%,水解度23.09%;此时,DPPH自由基清除率EC50为0.4mg/mL,.OH清除率EC50为0.7mg/mL。     

猪腿纤维蛋白的热致胶凝与功能性质(英文)

本实验探讨了蛋白浓度和 pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重以及热致胶凝性质的影响。在 0.6mol/L、pH6.0 的 NaCl 溶液中,纤维蛋白的胶凝性最强,凝胶强度随着蛋白浓度的增加而增加。然而,蛋白浓度的增加对蒸煮失重和蛋白质溶解度产生不利影响。猪腿纤维蛋白在 4℃贮存一段时间后,其溶解度有所增加。实验结果表明:pH 值对猪腿纤维蛋白的溶解度、凝胶强度、蒸煮失重和粘弹性都有一定的影响。在 pH6.0 时,蛋白的凝胶强度最大,而在 pH7.0 时,蛋白溶解度最大,蒸煮失重最小。     

Effect of acetylation and succinylation on solubility profile, water absorption capacity, oil absorption capacity and emulsifying properties of mucuna bean (Mucuna pruriens) protein concentrate

Mucuna protein concentrate was acylated with succinic and acetic anhydride. The effects of acylation on solubility, water absorption capacity, oil absorption capacity and emulsifying properties were investigated. The pH-dependent solubility profile of unmodified mucuna protein concentrate (U-mpc) showed a decrease in solubility with decrease in pH and resolubilisation at pH values acidic to isoelectric pH (pH 4). Apart from pH 2, both acetylated mucuna protein concentrates (A-mpc) and succinylated mucuna protein concentrate (S-mpc) had improved solubility over the unmodified derivative. Acylation increased the water absorption capacity (WAC) at all levels of ionic strength (0.1-1.0 M). WAC of the protein samples increased with increase in ionic strength up to 0.2 M after which a decline occurred with increase in ionic strength from 0.4-1.0 M. When protein solutions were prepared in salts of various ions, increase in WAC followed the Hofmeister series in the order: NaSCN < NaClO4 < NaI < NaBr < NaCl < Na2SO. Acetylation improved the oil absorption capacity while the lipophilic tendency reduced the following succinylation. Emulsifying capacity increased with increase in concentration up to 2, 4 and 5% w/v for U-mpc, A-mpc and S-mpc, respectively, after which an increase in concentration reduced the emulsifying capacity. Both acetylation and succinylation significantly (P < 0.05) improved the emulsifying capacity at pH 4-10. Initial increase in ionic strength up to 0.4 M for U-mpc and 0.4 M for A-mpc and S-mpc increased the emulsion capacity progressively. Further increase in ionic strength reduced emulsion capacity (EC). Contrary to the effect of various salts on WAC, increase in EC generally follows the series Na2SO4 < NaCl < NaBr < NaI < NaClO4 < NaSCN. At all levels of ionic strength studied, S-mpc had a better emulsifying activity (EA) than both A-mpc and U-mpc. EA and emulsifying stability (ES) were pH-dependent. Maximum EA and ES were recorded at pH 10. ES of protein derivatives were higher than those of U-mpc in the range of pH 4-10 but lower at pH 2. Studies revealed that both A-mpc and S-mpc had better ES and EA than the unmodified derivative when protein solutions were prepared in salts of various anions.